/Engine/Source/Runtime/GeometryCore/Public/DynamicMeshEditor.h
For a 'tube' of triangles connecting loops of corresponded vertices, set smooth normals such that corresponding vertices have corresponding normals
void SetTubeNormals ( const [TArray](API\Runtime\Core\Containers\TArray)< int > & Triangles, const [TArray](API\Runtime\Core\Containers\TArray)< int > & VertexIDs1, const [TArray](API\Runtime\Core\Containers\TArray)< int > & MatchedIndices1, const [TArray](API\Runtime\Core\Containers\TArray)< int > & VertexIDs2, const [TArray](API\Runtime\Core\Containers\TArray)< int > & MatchedIndices2 )